1. Field of the Invention
The invention pertains generally to fiber optics, and more particularly to a fiber optic connector housing, a fiber optic receptacle, various accessories for electro-optic modules which include fiber optic connector housings and corresponding optical assemblies.
2. Description of the Related Art
Those engaged in the manufacture and use of communication systems, e.g., systems for communicating voice, video and/or data, have become increasingly interested in using fiber optic cables as transmission media in such systems. This interest is stimulated by the fact that the potential bandwidth (or information-carrying capacity) of optical fibers is extremely high. In addition, communication systems employing fiber optic cables are resistant to electromagnetic interference, which sometimes plagues systems employing electrical cables as transmission media. Moreover, communication systems employing fiber optic cables are considered more secure than systems employing electrical cables because it is generally more difficult for unauthorized personnel to tap or access a fiber optic cable without being detected.
An exemplary communication system employing a fiber optic cable as a transmission medium is one which includes, for example, two or more computers, e.g., mini-computers, with each adjacent pair of mini-computers being interconnected by a fiber optic cable which includes two optical fibers, i.e., a transmit optical fiber and a receive optical fiber. Obviously, each mini-computer generates and receives information, i.e., data, in electrical form. Consequently, each mini-computer is also provided with an electro-optic module, typically mounted on a printed circuit board or printed circuit card of the mini-computer, which converts the electrical signals generated by the mini-computer into optical signals, which are transmitted to the adjacent mini-computer via the transmit optical fiber. In addition, the electro-optic module converts optical signals communicated to the mini-computer via the receive optical fiber into corresponding electrical signals.
An electro-optic module 10, typical of the type referred to above, is depicted in FIG. 1 and includes a housing 20 containing a transmitter optical subassembly (TOSA) 30 (not shown), a receiver optical subassembly (ROSA) 40 (not shown) and a pinned ceramic substrate 50 (not shown) bearing a number of semiconductor integrated circuit devices, with the pins 55 of the ceramic substrate protruding from the housing 10. The TOSA 30, which is electrically connected to certain of the semiconductor integrated circuit devices (hereinafter denoted the TOSA ICs), includes an electro-optic transducer, such as a semiconductor laser, which serves to convert electrical signals generated by the TOSA ICs into corresponding optical signals. The TOSA 30 also includes a lens (not shown) and a hollow cylinder (for the sake of convenience, hereinafter termed a bore) 35, which bore protrudes from the housing 10, with the lens serving to focus the light produced by the semiconductor laser onto the end of a transmit optical fiber which is to be inserted into the bore 35. Similarly, the ROSA 40, which is also connected to certain of the semiconductor integrated circuit devices (hereinafter denoted the ROSA ICs), includes an electro-optic transducer, such as a PIN photodiode, which serves to convert optical signals received by the photodiode into corresponding electrical signals, which are communicated to the ROSA ICs. The ROSA 40 also includes a bore (hollow cylinder) 45, which protrudes from the housing 10, into which a receive optical fiber is to be inserted, the receive optical fiber serving to communicate optical signals to the PIN photodiode.
The transmit and receive optical fibers, referred to above, are depicted in FIG. 1 and are denoted, respectively, by the numbers 60 and 70. As is conventional, and as shown in FIG. 1, each of these optical fibers is encased in one or more protective plastic sheaths, and each of these optical fibers extends into a ferrule (not shown). To prevent optical losses, it is important that the ferrule containing the transmit optical fiber 60 be inserted into the bore 35 so as to bring the transmit optical fiber into precise alignment with the semiconductor laser and corresponding lens of the TOSA 30. Similarly, it is important that the ferrule containing the receive optical fiber 70 be inserted into the bore 45 so as to bring the receive optical fiber into precise alignment with the PIN photodiode of the ROSA 40. If, for example, the transmit and receive optical fibers are single mode fibers, then the accuracy of each of these alignments must typically be to within one micrometer or less.
One set of devices which permits the achievement of micrometer-accurate alignment is also depicted in FIG. 1. That is, as shown in FIG. 1, such alignment accuracy is achievable by inserting the ferrule containing the transmit optical fiber 60 into a plug frame (not shown) which, in turn, is inserted into an individual fiber optic connector housing (FOCH) 80. Similarly, the ferrule containing the receive optical fiber 70 is inserted into a plug frame (not shown) which, in turn, is also inserted into an individual FOCH 90. As also shown in FIG. 1, each of the individual FOCHs is, for example, of the so-called push-pull type available from NTT (Nippon Telegraph and Telephone Corporation, Tokyo, Japan) and referred to as SC-01 straight plug connector. As depicted, each such SC-01 connector is hollow and generally rectangular in cross-section and has length, height and width dimensions of, respectively, 1.000 inches (25.4 mm), 0.356 inches (9.05 mm) and 0.293 inches (7.45 mm). Each such SC-01 connector is also to be inserted into a common receptacle housing (described below), which serves as the mechanism for achieving the above-described alignment. To achieve proper orientation of the individual FOCHs relative to this common receptacle housing, the individual FOCH 80 includes a key 82 on a side surface, and the individual FOCH 90 includes a key 92 on a side surface, which keys are to be received in corresponding keyways in the common receptacle housing. In addition, for reasons explained below, the front end of the individual FOCH 80 includes symmetrical, inclined surfaces 84 and 85, and the top and bottom surfaces of the FOCH 80 include symmetrical apertures 86 (shown) and 87 (not shown). Similarly, the front end of the individual FOCH 90 includes symmetrical, inclined surfaces 94 and 95, and the top and bottom surfaces of the individual FOCH 90 include symmetrical apertures 96 (shown) and 97 (not shown). As explained below, it has been believed that the symmetries associated with these inclined surfaces and apertures are essential to achieving alignment accuracies of one micrometer or less.
To take into account manufacturing tolerances associated with the common receptacle housing and/or the individual FOCHs 80 and 90, while still assuring successful insertion of the individual FOCHs into the common receptacle housing, the devices depicted in FIG. 1 also include a separate adapter 100 of the type disclosed in U.S. Pat. No. 4,953,929, which is hereby incorporated by reference. This adapter 100, when connected to the individual FOCHs 80 and 90, permits successful insertion to be achieved while taking account of manufacturing tolerances because the adapter serves to maintain the individual FOCHs in a substantially side-by-side relationship while permitting the individual FOCHs to move relative to one another in at least four different directions. That is, as shown in FIG. 1, the adapter 100 includes a generally C-shaped clamp member 110, which is adapted to clamp onto individual FOCH 80, and a generally C-shaped clamp member 120, which is adapted to clamp onto individual FOCH 90. Each such clamp member includes tabs 105 intended to engage corresponding slots or openings in the individual FOCHs. In addition, the adapter 100 also includes a generally S-shaped flexible member 130 which extends between the clamp members 110 and 120. It is the clamp members 110 and 120 which serve to maintain the individual FOCHs in a substantially side-by-side relationship. On the other hand, it is the generally S-shaped flexible member 130 which permits the individual FOCHs to move relative to one another in at least four different directions.
The relative motions permitted by the generally S-shaped flexible member 130 are depicted in FIGS. 2a through 2h, with the arrows in these figures indicating the directions of the motions. For example, as depicted in FIGS. 2a and 2b, the flexible member 130 permits the individual FOCHs to be moved compressively and expansively toward and away from each other. In addition, as depicted in FIGS. 2c and 2d, the flexible member 130 permits each individual FOCH to be moved up or down relative to the other FOCH. Further, as depicted in FIGS. 2e and 2f, the flexible member 130 permits the individual FOCHs to be pivoted, relative to each other, about parallel axes 140 and 150, which are perpendicular to the plane of the paper containing FIGS. 2e and 2f. Moreover, as depicted in FIGS. 2g and 2h, the flexible member 130 permits each individual FOCH to be pivoted, relative to the other FOCH, about an axis 160 which extends between the individual FOCHs and is perpendicular to the axes 140 and 150.
It should be noted that all parts of the adapter 100 are conventionally of identical thickness which is, for example, 0.030 inches (0.76 mm). In addition, the width of each of the clamp members 110 and 120 is conventionally identical and is, for example, 0.276 inches (7.00 mm), while the height of each of the clamp members 110 and 120 is conventionally identical and is, for example, 0.356 inches (9.05 mm). Further, the width of the flexible member 130 is, for example, 0.142 inches (3.60 mm). Consequently, when the clamp members 110 and 120 are clamped onto the individual FOCHs 80 and 90, and if one takes into account the thicknesses of the vertical side walls of the clamp members and the width of the generally S-shaped flexible member 130, then it follows that the center-to-center spacing between the FOCHs, and therefore the center-to-center spacing between the ferrules contained in the FOCHs, is 0.5 inches (12.7 mm).
The common receptacle housing, referred to above, is depicted in FIG. 1 and denoted by the number 140. This receptacle housing is generally rectangular in outline and includes two longitudinally extending apertures 150 and 160, which are generally rectangular in cross-section and dimensioned to receive the individual FOCHs 80 and 90. In addition, the aperture 150 includes a keyway 155 adapted to receive the key 82 of the individual FOCH 80, while the aperture 160 includes a keyway 165 adapted to receive the key 92 of the individual FOCH 90.
As also shown in FIG. 1, a first pair of clips 170, interconnected by a wall 177, is provided for insertion into the rear of aperture 150, while a second pair of clips 180, interconnected by a wall 187, is provided for insertion into the rear of aperture 160. The longitudinal extent of the first and second pairs of clips 170 and 180 in the apertures 150 and 160 is chosen in relation to the lengths of the keyways 155 and 165 so that the keyways extend fully to the front ends of the first and second pairs of clips. In addition, the first pair of clips 170 includes symmetrical, inclined camming surfaces 174 and 175 which are adapted to engage the symmetrical, inclined surfaces 84 and 85, as well as the symmetrical apertures 86 and 87, of FOCH 80. Similarly, the second pair of clips 180 includes symmetrical, inclined camming surfaces 184 and 185 which are adapted to engage the symmetrical, inclined surfaces 94 and 95, as well as the symmetrical apertures 96 and 97, of FOCH 90.
As is evident from FIG. 1, the wall 177, interconnecting the first pair of clips 170, includes an aperture 178, centrally located between the clips 170, which is adapted to receive bore 35. Similarly, the wall 187, interconnecting the second pair of clips 180, includes an aperture 188, centrally located between the clips 180, which is adapted to receive bore 45.
When assembled, the above-described elements permit the ferrules containing the optical fibers 60 and 70 to extend into the bores 35 and 45 and to be properly aligned to within micrometer tolerances. That is, in the course of assembly, the adapter 100 is used to interconnect the individual FOCHs 80 and 90 by applying the clamp member 110 to the FOCH 80 and the clamp member 120 to the FOCH 90. In addition, the first and second pairs of clips 170 and 180 are inserted into the rear ends of the longitudinally extending apertures 150 and 160 of the receptacle housing 140, and the bores 35 and 45 are then inserted into the centrally located apertures 178 and 188 of the first and second pairs of clips. The front ends of the interconnected FOCHs 80 and 90 are then inserted into the front ends of the longitudinally extending apertures 150 and 160, with the key 82 entering the keyway 155 and the key 92 entering the keyway 165. These keyways 155 and 165, which extend all the way to the first and second pairs of clips 170 and 180, serve to guide the FOCHs 80 and 90 to these pairs of clips and have been believed to be essential to achieving micrometer-accurate alignment.
When the front ends of the FOCHs 80 and 90 contact the first and second pairs of clips 170 and 180, the symmetrically inclined camming surfaces 174 and 175 of the first pair of clips 170 engage the symmetrically inclined surfaces 84 and 85 of the FOCH 80, and the symmetrically inclined camming surfaces 184 and 185 of the second pair of clips 180 engage the symmetrically inclined surfaces 94 and 95 of the FOCH 90. As the FOCHs 80 and 90 are inserted more deeply into the apertures 150 and 160, the camming action effected by the camming surfaces serves to align the FOCHs 80 and 90, and therefore the ferrules contained in these FOCHs, relative to the bores 35 and 45 even as the ferrules enter these bores. As insertion continues, the clips 170 come to extend into the symmetrical apertures 86 and 87 of the FOCH 80 to thereby engage, and grip, the underlying plug frame, while the clips 180 come to extend into the symmetrical apertures 96 and 97 of the FOCH 90 to thereby also engage, and grip, the underlying plug frame. As a consequence, these plug frames and corresponding transmit and receive optical fibers are maintained in proper alignment relative to the bores 35 and 45 and to the corresponding semiconductor laser/lens combination and PIN photodiode associated with, respectively, the TOSA 30 and ROSA 40.
It must be emphasized that it has been believed that the above-described assembly procedure achieves micrometer-accurate alignment because the keyways 155 and 165, which extend all the way to the clips 170 and 180, serve to maintain the FOCHs in proper alignment relative to the clips up until the moment the clips engage the FOCHs, and that only such keyways are capable of achieving such alignment. In addition, it has also been believed that micrometer-accurate alignment is achieved because the forces exerted by the clips 170 and 180 on the FOCHs during the insertion procedure are symmetrical, and that such symmetrical forces can only be achieved by employing FOCHs having symmetrically inclined surfaces and apertures. Moreover, it has been believed that any deviation from such symmetrically inclined surfaces and apertures will necessarily lead to asymmetrical forces being exerted on the FOCHs, leading to unacceptably large misalignments between the transmit and receive optical fibers and, respectively, the semiconductor laser/lens combination and PIN photodiode.
It should be noted that the assembly procedure, described above, is relatively complex and adds substantially to the cost of the resulting optical assembly, and that there has long been a desire to reduce this cost.
Significantly, a number of new communication systems employing fiber optic links have been proposed. One such system, depicted in FIG. 3, serves to connect a plurality of devices in a so-called star network, using fiber optic links. As shown in FIG. 3, these devices include, for example, a direct access storage device (DASD), which includes one or more hard disks. These devices also include, for example, a printer and central processing units (CPUs) contained in, for example, personal computers or engineering work stations. In addition, these devices include, for example, a number of end stations, such as computer terminals, and a terminal concentrator, which allows the computer terminals to communicate with the CPUs in the star network.
Yet another proposed communication system employing fiber optic links is depicted in FIG. 4. In this system, a number of devices are connected to each other, via fiber optic links, through a central optical switch. This system includes, for example, CPUs, a DASD, computer terminals, and a shared memory, consisting of semiconductor memory. In addition, and as depicted in FIG. 4, this system could also include one or more telephone systems.
A number of standards have been proposed in connection with the communication systems depicted in FIGS. 3 and 4 and described above. For example, the personal computers and/or engineering work stations containing the CPUs mentioned above conventionally have brackets which hold printed circuit cards. Each such bracket also includes an opening or slot which permits the insertion of an input/output cable, such as an electrical cable or a fiber optic cable. If such a personal computer or engineering work station were to be included in one of the communication systems, described above, then this personal computer or engineering work station would have to include an electro-optic module and, for example, a common receptacle housing, of the type described above, mounted on a printed circuit card of the personal computer or engineering work station. A fiber optic connector housing which included, for example, two individual FOCHs 80 and 90 connected by an adapter 100, which individual FOCHs contain transmit and receive optical fibers, would then have to fit into the relevant slot in order to insert the fiber optic connector housing into the common receptacle housing, and thereby connect the corresponding fiber optic cable to the electro-optic module. However, to achieve consistency with other existing standards, a new standard has been proposed by the X3T9.3 committee of the American National Standards Institure (ANSI), which may also be adopted by the International Electrotechnical Commission (IEC), requiring the slot to be 0.293 inches (7.45 mm) high and 0.856 inches (21.75 mm) wide. Moreover, this new proposed standard also requires the center-to-center spacing between the ferrules, and therefore the center-to-center spacing between the individual FOCHs, to be 0.5 inches (12.7 mm). However, while an adapter 100 in combination with two individual FOCHs 80 and 90 can achieve a center-to-center spacing of 0.5 inches, the height of, for example, NTT SC-01 FOCHs is conventionally 0.356 inches (9.05 mm), which is greater than the the height of the slot specified in the proposed standard. As a consequence, such a combination could not be inserted into such a slot. If, on the other hand, the individual FOCHs were to be rotated by ninety degrees, so that the height and width of the individual FOCHs were to be interchanged, and if the adapter 100 were to be manufactured so that the height and width of the adapter were to be interchanged without reducing the width of the flexible member, then a combination of such an adapter and two such individual FOCHs would fit into the slot defined by the proposed standard. Unfortunately, by virtue of the thicknesses of the side walls of the clamp members 110 and 120 of such an altered adapter 100, the center-to-center spacing between the individual FOCHs would be 0.563 inches (14.3 mm), which violates the center-to-center spacing of 0.5 inches required by the proposed standard. It should also be noted that reducing the width of the flexible member, to achieve a center-to-center spacing of 0.5 inches, is not a viable option because any such width reduction significantly degrades the flexibility, and therefore functionality, of the flexible member.
Thus, those engaged in the development of fiber optics have sought, thus far without success, combinations of individual FOCHs and corresponding adapters, and combinations of common receptacle housings and pairs of clips, which require less assembly, and therefore lead to corresponding optical assemblies which are less costly. In addition, those engaged in the development of fiber optics have sought, thus far without success, combinations of at least two individual FOCHs and corresponding adapters which meet the height, width and center-to-center spacing requirements specified in the proposed ANSI standard, discussed above.